Vehicle manufacturers are introducing speech recognition technology into vehicles for both voice command control of vehicle equipment and as a natural language interface to wider internet-based services. This technology currently performs well with a close-talking microphone but performance drops significantly when the microphone is placed at a distance from the speaker. Sound from the speaker's mouth takes a multi-path route to the microphone because the sound is reflected off different in-vehicle surfaces and reverberated before finally entering the microphone capsule. The microphone also has a characteristic electrical response to the acoustic waves and this cascade of systems leads to distortion of the original speech, making the function of speech recognition more difficult. A similar problem arises during mobile (cellular) telephone conversations when the microphone is remote from the speaker's mouth.
Audio and speech content reproduction technology is well established in the modern vehicle but the quality and intelligibility of the reproductions is often poor. Original recordings are made in environments that are acoustically very different from that inside the vehicle and sounds that appeared bright in the recording studio may be dulled inside the vehicle because the in-vehicle environment acoustically damps out critical component frequencies. Other frequency components of sound may also be boosted by the acoustic environment inside the vehicle to the point that they dominate and create an unnatural or unbalanced listening experience for the user.
Audio capture and reproduction systems offer manufacturers potential to add new value to their vehicles and it would be desirable to provide such systems with the ability to model and correct for the distortion of sound in the vehicle by estimation of acoustic channels.